Maximizing fuel efficiency in modern vehicle design is a prime concern of engineers. One area that contributes to fuel efficiency of a vehicle is vehicle aerodynamics. The pattern of air movement over a vehicle has been closely scrutinized over time and is well understood. More recently, the flow of air beneath a vehicle has also been closely scrutinized. In one aspect of vehicle underbody design, when more surfaces can be made consistently smooth, underbody aerodynamics is improved.
For years, tractor trailer vehicles and heavy duty pick-up trucks have stored spare tires (including a wheel rim) on the vehicle underbody. This type of spare tire storage is becoming more prevalent on passenger vehicles as well because more interior space can be reserved for storage of personal items or cargo.
There is a continuing debate over the desirability of using, in passenger vehicles, a full sized spare tire as compared to a smaller temporary spare tire. On one hand, the full sized spare tire can be switched with a damaged tire and used indefinitely while providing the same performance characteristics as the remaining three tires. On the other hand, use of a temporary spare, when in storage, takes up a small amount of storage room and is light, thus, increasing the vehicle's overall fuel efficiency. Each spare tire type lacks the advantages of the other type.
When a spare tire is secured to a vehicle underbody, either type of spare tire can be held by a known hoist or clamping system. However, what is desired is a way of providing a consistent smooth air flow surface on the underside of the vehicle, no matter which type of spare tire is used so superior vehicle aerodynamics can be maintained.